You didn't give many details so these are things to consider - what water are you using for your tank & water changes? How much water are you replacing when you perform a water change? If it's only 10%, that is not a sufficient quantity to turn your problem around. What's your bio load, the quantity & frequency of feeding? Do you use charcoal? You might have insufficient filtration or water movement. Do you have a sufficient cleanup crew? Are all inhabitants accounted for? A dead critter coupled with a subpar cleanup crew can definitely ruin a good tank day. Hope this helps.

Sorry
I have a 55 breeder with a 30 gallon sump. Approx 80# of live rock no fish or clean up crew. After the last time we moved all fish and corals made the move all went well after a few months every thing died. I kept the tank up and running adding top off water and water changes once a month of 20 gallons. I don't use charcoal. Run reef octopus 110 in the sump phosban reactor with gfo I have a 4 stage ro/di system. The local fish store was too high priced on new fish so I took a break for a while. A new place opened up in my neighborhood so now I'm lookin to get things going again before momma sells it.

The actions I have started to get things going back in the right direction are as follows.
I checked ph ok nitrites ok ammonia ok salt .025 ok nitrates over 160.
I cleaned the sump skimmer water change of 30 gallons twice over the pAst week just checked nitrates 10 minutes ago it's between 60-80. I'm getting ready to drain the tank rinse off the live rock in fresh salt water remove the sand and replace with new about 40 lbs and refill with fresh salt water yes or no?????

Hopefully others will chime in on this. Taking into consideration all that you have done, the first thing that I would do if it were me, would be to get a cleanup crew appropriate for a 55 gallon... Turbo snails, both blue and red legged hermits, nassarius snails, Emerald crabs as well as Porcelain crabs, and a cleaner shrimp. There are places online that can ship to your door. I just got notification yesterday from Aquariumdepot .com of a cleanup crew sale they were having.

I know this is an old thread but I had my maxijet fail that was running my hang on refugium. It was off for a few days. My old tank had huge nitrates, and I wound up changing 70 gallons on my 75 gallon tank in a week and a half. That worked to get the nitrates back down.

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